[Haskell] Image manipulation
simonmarhaskell at gmail.com
Thu Nov 1 05:10:46 EDT 2007
Stefan O'Rear wrote:
> On Wed, Oct 31, 2007 at 10:58:40AM +0100, Ketil Malde wrote:
>> Bjorn Lisper <lisper at it.kth.se> writes:
>>> Wait, Jerzy. Haskell implementations do not have to be lazy as long as they
>>> preserve the more abstract semantics. Optimistic evaluation has been
>>> considered, for instance by Robert Ennals.
>> I'm not sure if the GC hack proposed by Wadler¹ that lets the garbage
>> collector replace "fst (a,b)" with "a" (and similar for other unchecked
>> selectors) counts as optimistic evaluation, but I wonder what the
>> status of this is. GHC doesn't seem to do it, and I wonder if there
>> is any particular reason? Too specific?
> GHC nominally does do it (look for 'selector thunks' in the RTS and
> commentary), but it doesn't work and we don't know why.
GHC HEAD has a fix for the example in that ticket, and 6.8.1 has a
workaround (I bumped the recursion depth limit enough to make it run in
constant space). Do you have an example that still doesn't work,
particularly with the HEAD?
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